The present invention relates to vehicle transmissions, and more particularly to a system for improved performance of damper hubs in dry plate clutches.
Dry plate clutches are used in manual and automated vehicle transmissions to facilitate start-off from rest and disengage the transmission from the engine at gear shifts. In general, there is a damper hub integrated in a dry plate clutch. Adequately designed, this damper hub reduces torsional vibrations from the engine and spares the transmission. A damper hub usually has a number of helical springs arranged circumferentially on the driven disc that transfers torque from the engine flywheel to the input of the transmission. Some designs are shown in DE-10220205.
For heavy road vehicles, such as heavy trucks and buses, there has been a long-lasting trend towards more powerful engines. This poses technical challenges on the damper hubs to withstand higher engine torques and more severe torsional vibrations. For conventional simple damper hubs there is a limit on how large engine torques that can be handled. That limit has been increased by the use of helical springs of larger diameter that are located on a larger radius from the axis of rotation of the damper hub. Further such increases would imply a reduction of the friction lining area of the driven disc. That would, in turn, reduce the energy-absorbing ability as well as the life of the clutch. An alternative would be to increase the outer diameter of the clutch, which would make it difficult to fit the clutch in the chassis. Thus, these would be impractical ways to increase the torque capacity of the damper hub.
For higher engine torques, twin-disc clutches are frequently used. A typical design is shown in U.S. Pat. No. 6,782,985. Another example is shown by U.S. Pat. No. 1,935,459. In a twin-disc clutch there are two driven discs connected in parallel. Each of these discs has a damper hub. Thereby, each damper hub will be subjected to half the engine torque. Hence, very high engine torques can be handled by a twin-disc clutch. Unfortunately, twin-disc clutches are in general less attractive in terms of length, weight and cost. Moreover, compared to single-disc clutches they are more difficult to control. That makes twin-disc clutches unsuited for automated transmissions.
Another way to handle the torsional vibrations of powerful engines is by using a dual mass flywheel. In such a design, the flywheel is divided into two parts with a resilient damper in between. One design can be seen in WO-9427062. In a dual mass flywheel the damper springs can be located in a very efficient way. Thereby, it has the potential to handle large engine torques. It also allows the use of a single-disc clutch, which is of advantage for automated transmissions. On the other hand, dual mass flywheels are heavy and expensive. Since the flywheel is divided, the clutch is also likely to have reduced thermal capacity.
Another known solution for higher engine torques is to arrange two axially separated rows of springs in a single disc clutch. Thereby, the torsional vibration handling capacity of a twin-disc clutch is combined with the lower weight and cost along with ease of control of a single-disc clutch. Examples of such damper hubs in single disc clutches are disclosed in DE 19528319, WO9200470, U.S. Pat. No. 4,475,640, DE4040606 and U.S. Pat. No. 5,145,463. The cost for manufacturing these single-disc clutches are still higher compared to a conventional single-disc clutch with one row of springs. There is therefore a need to further slim the design. Another problem with known art is that two parallel rows of springs increases the axial length compared to a solution with a single row of springs.
So, there is a need for a single-disc dry plate clutch with increased ability to handle torsional vibrations but without the disadvantages regarding weight, cost and total axial length of prior art. In a first embodiment of the invention a design is provided where a torsional vibration damper hub for a vehicle clutch comprises a hub splined to a shaft; first and second inner annular plates rotatably fitted to an outer periphery of the hub, first and second pairs of outer annular plates arranged at both sides of said first and second inner annular plate respectively; first row of springs extending substantially in the clutch rotating direction and disposed in openings formed in said first inner annular plate and said first pair of outer annular plates; second row of springs extending substantially in the clutch rotating direction and disposed in openings formed in said second inner annular plate and said second pair of outer annular plates, each first and second pair of the outer annular plates being connected to the adjacent inner annular plate by said springs; said first and second pair of outer annular plate being connected to the hub; a torque input member including one single friction plate fixed to said first and second inner annular plate. The invention is characterized, according to an aspect thereof, in that the springs in said first row of springs arranged in one first axial level are axially overlapping the springs in said second row of springs arranged in a second axial level with the purpose to decrease a total axial length of said clutch. That will give a very compact design whose axial space requirements would not be significantly larger than for a conventional single-disc clutch.
In a second embodiment of the invention an axial distance between geometrical centres of one spring in said first row and one spring in said second row, is larger than one half of the outer diameter of said springs. In this context the diameter of said springs of said first and second row can be chosen to be substantially equal or substantially different, thus, in the latter case the axial total length of said clutch can be decreased even further.
In a further embodiment of said invention said damper hub is substantially identical to a dual damper hub in conventional twin-plate clutches. This embodiment of the invention can also be used in a torsional damper hub without having springs in a first and second row that are axially overlapping (as in the embodiment above), but instead having two rows of springs that are not axially overlapping. This would result in a fairly compact and cost-effective solution.
In a further embodiment of said invention said first and second row of said springs are arranged on a substantially same radius from centre of rotation of said clutch. Arranging said rows on the same radius would give the opportunity to maximize the possibility to handle high engine torques by the clutch.